This invention relates to a method for inspecting the qualities of a thin material film for use in a semiconductor device.
In semiconductor integrated circuit (IC) devices, thin films of a metal, a semiconductor, or an insulator are commonly used to form conductor layers, gate electrodes, gate indulating layers, or the like. In general, these films are formed by spattering, vapor-deposition, or chemical-vapor deposition (CVD) processes. In case such process conditions for making a thin material film are introduced into IC device manufacturing lines, it is important to carefully inspect and ascertain the quality of the thin film for the purpose of improving the yield of semiconductor IC devices. Ideally, it is desirable that such thin material films have no pinholes therein to obtain a good yield of IC devices. A thin material film having a large pinhole density will degrade the reliability of IC devices.
There are a number of ways for inspecting the quality of a thin material film. For example, pinhole inspection of an aluminum film over a semiconductor substrate has been carried out by directly counting the pinholes therein under a microscope. However, since this method counts pinholes in an aluminum film in a narrow limited scope of microscope, it has been difficult to determine the pinhole density in a short time. In addition, there is the copper decoration method which is applicable to thin insulating material film. Mary L. Long describes this method in his paper entitled "Quantitative Evaluation of Photoresist", on page 228, in the paper on Microminiaturization issued by Kodak Seminar in 1970. The method comprises the steps of applying a photoresist film having a predetermined thickness on the surface of a silicon substrate, baking the photoresist film at 150.degree. C. for about 30 minutes, immersing the structure obtained by the above steps into an electrolyte with the substrate being connected to a positive electrode of a battery and an electrode in the electrolyte being connected to a negative electrode of the battery, and then counting the copper deposited portions in the pinholes therein under microscope. However, it is difficult to accurately count the pinholes, since copper material sometimes deposits on the surface of a thin film in addition to the inside of the pinholes therein. Furthermore, this method has required a long time to deposit a copper film, and it is not suitable to inspect the defects of thin metal film.